The use of natural fiber materials in medical and industrial applications has been found to be highly advantageous in situations where a non-linting, absorbent pad or wiper is required. A material that has been employed in such applications is found in the Webril material from the Kendall Company of Massachusetts. The Webril material is a compressed, mercerized cotton fibrous batt. The mercerization process involves the swelling of the natural cotton's ribbon like profile into an approximately round profile of larger diameter. Typically, caustic washes are utilized while the cotton batt is under tension to induce the swelling of the cotton fiber. Because of the use of a caustic solution, it is necessary to subsequently treat the cotton material with an acidic solution so as to neutralize the material and render it useable. A number of complicated steps are required to successfully perform the process, with a significant amount of environmentally harmful effluent being produced.
In the interest of forming natural fiber nonwoven pads or wipers without the by-products of mercerization, the application of a resin binder in conjunction with hydroentanglement was explored as evidenced by U.S. Pat. Nos. 2,862,251, 3,033,721, 3,769,659, and 3,931,436 to Kalwaites et al., and U.S. Pat. Nos. 3,081,515 and 3,025,585 to Griswold et al, the disclosures of which are herein incorporated by reference. The application of resin binder was found to have a deleterious effect on the softness of the corresponding nonwoven fabric.
The findings by Evans, U.S. Pat. No.3,485,706, the disclosure of which is herein incorporated by reference, suggested that the impedance of energetic water streams on a fibrous batt could produce a nonwoven fabric by the entanglement of those fibers with one another through the depth of the fibrous batt, thus obviating the need for a resin binder. However, the action of the water streams upon the fibrous batt and the action of entangling the fibers result in a fabric having significantly decreased bulk, and correspondingly decreased tactile and ductile softness.
Various attempts have been made in order to obtain a durable natural fiber nonwoven fabric while maintaining sufficient strength and softness. In U.S. Pat. No. 5,849,647 to Neveu, herein incorporated by reference, a hydrophilic cotton stratified structure is formed by interceding an air-randomized core in between two previously formed, highly fiber oriented carded layers. The stratified layers are subsequently treated with a soda liquor which is then boiled off to render an integrated structure. While a cotton structure performed by the manner described can render an ultimate material that is low linting, the material must undergo substantial processing in the forming of separate and distinct layers and the juxtaposition of those layers during the caustic integration step. U.S. Pat. No. 4,647,490 to Bailey et al., the disclosure of which is herein incorporated by reference, formed an apertured, cotton fiber nonwoven material by hydroentanglement induced by oscillating water streams. In the Bailey process, the fibers of the fibrous batt are washed down and through the fibrous batt in order to entangle the fibers and form apertures in the fabric. U.S. Pat. No. 4,426,417 to Meitner et al., the disclosure of which is herein incorporated by reference, incorporated the use of thermoplastic meltblown during the formation of a fibrous batt as a means for attaining the loft for absorbency and maintain sufficient physical strength by bonding the fibers together. As the nature of the Meitner process is based upon the total and effective binding of the fibers to the thermoplastic meltblown there are potential issues with unbound or loosely bound fibers being disengaged from the meltblown.
Given the prior art attempt to form a non-linting, soft and yet strong absorbent materials, there remains a need for a nonwoven fabric exhibiting these characteristics and yet is formed in an expeditious and uncomplicated manner.
A method for forming a suitable nonwoven fabric meeting the aforementioned requirements has been identified in the application of fluidic energy such that a single fibrous batt is imparted with a highly entangled surface of outer fibers while retaining the loft and absorbency of a lightly entangled central layer of core fibers.